1. Field of the Invention
The present invention relates to a thin film transistor structure, and more particularly, to a thin film transistor structure of a pixel which can be applied to a lower substrate of a liquid crystal display panel.
2. Description of the Prior Art
Manufacturing processes of thin film transistor liquid crystal display (TFT LCD) panels include array processes and color filter processes, wherein required electrode substrates, which include voltage-controlled thin film transistors for transmitting signals, are formed in the array processes. Refer to FIG. 1, which is a schematic diagram illustrating a thin film transistor in the prior art. As shown in FIG. 1, a first metal layer 10 serves as a gate electrode 12, and an amorphous silicon layer 14 is formed on the first metal layer 10 and partially overlaps the first metal layer 10. A second metal layer 16 is disposed on the first metal layer 10, and the second metal layer 16 includes a drain electrode 18, a source electrode 20 and a data line 22. The drain electrode 18 is T-shaped and extends to partially overlap the amorphous silicon layer 14. The source electrode 20 is disposed on the amorphous silicon layer 14, and the source electrode 20 is U-shaped and corresponds to the drain electrode 18. Furthermore, the source electrode 20 is connected to the data line 22 which is transversely above the first metal layer 10. In addition, a pixel electrode layer 24 is disposed on the drain electrode 18 and is electrically connected to the drain electrode 18 through a via hole 26.
When a photolithographic process of the array processes is performed, deviation may occur due to slight vibration of an exposure machine in a light exposure process. As shown in FIG. 2, the location of the drain electrode 18 shifts downwardly in the longitudinal direction with respect to that in FIG. 1. As an area of an overlapping region between the amorphous silicon layer 14 and the drain electrode 18 formed by the second metal layer 16 varies, a parasitic capacitor (Cgd) between the gate electrode 12 and the drain electrode 18 would vary. As a result, feed-through voltage of the pixel electrode which is caused by the parasitic capacitor would accordingly vary due to variance of the parasitic capacitor, and some undesired effects such as mura and flicker may occur in local regions of the liquid crystal display panel.
Therefore, for the aforementioned problems, a thin film transistor structure is provided in the present invention to withstand deviation caused by vibration of the machine in the photolithographic process.